The present invention relates to an oxidation process for the production of S,S,S-tributylphosphorotrithioate.
S,S,S-tributylphosphorotrithioate is known to be useful as a defoliant. This defoliant is typically produced by reacting phosphorus trichloride with butyl mercaptan to form S,S,S-tributylphosphorotrithioite (phosphite). The phosphite is then oxidized to form the corresponding S,S,S-tributylphosphorotrithioate.
Processes for the production of phosphite are disclosed, for example, in U.S. Pat. Nos. 2,682,554; 2,943,107; 3,885,002 and 5,183,916.
Processes for the oxidation of phosphite to form the corresponding S,S,S-tributylphosphorotrithioate are disclosed in U.S. Pat. Nos. 2,943,107; 3,885,002 and 5,189,195. In the process disclosed in U.S. Pat. No. 2,943,107, the oxidizing agent is selected from air, molecular oxygen, peroxide, persulfates and chlorine water. The oxidizing agent for the process of U.S. Pat. No. 3,885,002 is molecular oxygen itself or in the form of air. In the process described in U.S. Pat. No. 5,189,195, peroxide was used as the oxidizing agent.
The disadvantage of each of these known oxidizing agents is the need to treat the crude oxidation product to improve the purity of the S,S,S-tributylphosphorotrithioate. These known processes require at least two (and often three) phase separation treatments to obtain a high purity product. Multiple extractions result in lost product and decreased yield. Such purification treatments also increase production time and expense.
Perborates and percarbonates are known materials. Sodium perborate is a large scale industrial chemical which is used as a source of active oxygen in detergents, as an alternative to various forms of chlorine for fiber bleaching, and as a mild antiseptic and mouthwash. Sodium perborate has also been investigated as a possible oxidizing agent for the production of azo compounds from aniline as described in S. M. Mehta and M. V. Vakilwala, J. Am. Chem. Soc., 74, 563 (1952) and L. Huestis, J. Chem. Ed., 54, 327 (1977) and for alkenylboronic acids as described in D. S. Matteson and R. J. Moody, J. Org. Chem., 45, 1091 (1980). To date, however, perborates and percarbonates have not been used to oxidize materials such as S,S,S-tributylphosphorotrithioite.